Method for regulating viscosity of alkane phase change microcapsule suspension by temperature change rate

Abstract

The application belongs to the field of functional material preparation, and discloses a method for regulating the viscosity of paraffin phase change microcapsule suspension by temperature change rate. First, a paraffin phase change microcapsule with smooth appearance and uniform particle size is prepared by using in-situ polymerization, and then a stable phase change microcapsule suspension is prepared by using a two-step method. The real-time temperature in the viscosity test is controlled by a heating table, the power of the heater is changed, the relationship between the viscosity of the microcapsule suspension and the temperature is tested under different heating rates, and the results show that the viscosity of the phase change microcapsule suspension will change in the phase change process of the core material, and the average viscosity of the suspension in the phase change temperature zone decreases with the increase of the heating rate. The relationship between the viscosity of the microcapsule suspension and the temperature is changed by changing the temperature change rate, so that the viscosity of the phase change microcapsule suspension in the phase change temperature zone is regulated.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of functional material preparation, and discloses a method for regulating viscosity of an alkane phase change microcapsule suspension by using temperature change rate. BACKGROUND

[0002] Paraffin can absorb and release a large amount of latent heat in the process of liquid-solid phase transition. The paraffin phase change microcapsule suspension obtained by mixing the phase change microcapsules formed by wrapping paraffin with a high molecular film-forming material and the traditional heat exchange working medium can not only solve the transportation problem of the paraffin phase change material, but also has the functions of energy storage and release, and is a new type of heat exchange working medium.

[0003] It is known that the performance of a heat exchange working medium must be evaluated by taking into account the energy transport characteristics and flow resistance characteristics of the pipeline flow, that is, the viscosity characteristics, so the viscosity of the heat exchange working medium plays a crucial role in the heat exchange process. Compared with the traditional working medium, the paraffin phase change microcapsule suspension can strengthen heat exchange due to the large amount of latent heat absorbed or released by the core material in the phase change process. However, in the calculation of the heat exchange strengthening of the phase change microcapsule suspension, the viscosity value at a certain temperature is usually used instead of the average viscosity value in the phase change process, which may cause the calculation result to deviate from the actual situation. In addition, the research on the effect of temperature on the phase change microcapsule suspension is generally limited to the single-phase category, and there is no definite conclusion on whether the solid-liquid phase change characteristics of the core material of the phase change microcapsule will affect the viscosity of the microcapsule suspension. SUMMARY

[0004] In order to solve the above-mentioned shortcomings and deficiencies of the prior art, the purpose of the present application is to provide a method for regulating the viscosity of an alkane phase change microcapsule suspension by using temperature change rate. The method uses an in-situ polymerization method to prepare paraffin phase change microcapsules with smooth appearance and uniform particle size, and a two-step method is used to obtain a stable paraffin phase change microcapsule suspension. The relationship between the viscosity of the phase change microcapsule suspension and the shear rate is tested at a certain temperature. The viscosity of the suspension is measured every 0.5-1℃ for 5-30min after being kept at a certain temperature range and shear rate. The relationship between the viscosity of the phase change microcapsule suspension and the temperature is tested at a certain temperature range, the same shear rate and different temperature change rates.

[0005] The present invention tests the relationship between the viscosity and temperature of the suspension at different heating rates within a certain temperature range. By analyzing the change in viscosity within the phase change temperature zone, the average viscosity value of the suspension at different heating rates is calculated. The results show that the solid-liquid phase change of the phase change microcapsule core material will affect the viscosity of the suspension, and the average viscosity of the microcapsule suspension in the phase change temperature zone decreases with increasing heating rate, thereby realizing the regulation of the average viscosity of the phase change microcapsule suspension by changing the heating rate.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for regulating the viscosity of an alkane phase-change microcapsule suspension by utilizing the temperature change rate comprises the following steps:

[0008] S1: Paraffin phase change microcapsules with smooth appearance and uniform particle size were prepared by in-situ polymerization, and then a stably dispersed phase change microcapsule suspension was prepared by a two-step method;

[0009] S2: Within the temperature range of 15-35°C, the relationship between the viscosity of the phase change microcapsule suspension and the shear rate is obtained by testing at a fixed temperature, and the shear rate A when the phase change microcapsule suspension is in a Newtonian fluid with constant viscosity is determined; within the temperature range of 15-35°C and the shear rate A condition, multiple viscosity values ​​of the phase change microcapsule suspension that change with time are measured after being kept warm at intervals of 0.5-1°C for 5-30 minutes, and the average value of the obtained multiple viscosity values ​​is taken as the viscosity of the suspension in a single-phase state, thereby obtaining the relationship between the viscosity of the suspension in a single-phase state and the temperature, that is, the η-T curve in the single-phase state; within the temperature range of 15-35°C, the shear rate A is used and the temperature rise rate is used to test the relationship between the viscosity of the phase change microcapsule suspension and the temperature, that is, the η-T curve under transient temperature change;

[0010] S3: According to the η-T curve in the single-phase state and the η-T curve under transient temperature change obtained in step S2, the phase change temperature section in which the viscosity of the suspension changes due to the phase change of the microcapsule core material is analyzed and determined, that is, the temperature from the beginning of melting of the corresponding microcapsule core material to the temperature at the end of melting; the average viscosity of the phase change microcapsule suspension in the phase change temperature section at different heating rates is calculated, and the relationship between the heating rate and the average viscosity of the phase change microcapsule suspension in the phase change temperature section is obtained, and the two show a linear relationship; the other parameters of the phase change microcapsule suspension are controlled to be the same, and the average viscosity of the phase change microcapsule suspension in the phase change temperature section is controlled by changing the heating rate.

[0011] The in-situ polymerization method of step S1 is specifically as follows: first, emulsifier is added into deionized water, and alkali solution is added dropwise to adjust the pH value to 7-10, then the emulsifier solution is fully dissolved under stirring at 200-500 rpm at 40-100℃; then, phase change material is poured into the reactor, and after shearing stirring at 50-90℃ and 100-300 rpm, oil-in-water emulsion is formed, then high molecular prepolymer is added, and the microcapsule emulsion of phase change material wrapped by high molecular shell is formed by reaction at 50-120℃; finally, the microcapsule emulsion is freeze-dried in a freeze dryer, and after grinding, the paraffin phase change microcapsule powder is obtained.

[0012] The two-step method of step S1 is specifically as follows: paraffin phase change microcapsules and anionic surfactant are weighed in a mass ratio of 1:3-0.5:1, and then added into deionized water together, stirred for 5-15 min, and then placed on a magnetic stirrer, stirred at 100-2000 rpm at 20-35℃ for 20-40 min, and finally ultrasonically treated for 0.5-3 h to obtain a phase change microcapsule suspension with a mass concentration of 5%-10%.

[0013] The phase change material is at least one of straight-chain alkane compounds and straight-chain alkane halides, and the high molecular prepolymer is one of melamine resin, formaldehyde resin or polymethyl methacrylate.

[0014] The multiple viscosity values of the phase change microcapsule suspension changing with time are measured after 0.5℃ interval and 10 min of incubation.

[0015] The particle size of the microcapsule of step S1 is 0.5-30 μm, and the viscosity test temperature range of step S2 is 10-35℃, the shear rate is 100-5000 s -1 , and the temperature change rate is 0.1-15℃ / min.

[0016] The calculation formula of the average viscosity of the phase change microcapsule suspension in the phase change temperature section is:

[0017]

[0018] wherein is the average viscosity of the phase change microcapsule suspension in the phase change temperature section, η is the viscosity of the phase change microcapsule suspension at different temperatures, T is the real-time temperature, T start is the temperature at the beginning of melting of the phase change microcapsule, and T end is the temperature at the end of melting of the phase change microcapsule.

[0019] The present application has the following advantages and effects relative to the prior art:

[0020] The present invention first determines the change in viscosity of the phase-change microcapsule suspension during the solid-liquid phase transition of the microcapsule core material; analyzes and calculates the average viscosity of the phase-change microcapsule suspension in the phase-change temperature zone; and controls the other parameters of the paraffin phase-change microcapsule suspension to be the same, thereby achieving regulation of the average viscosity of the suspension in the phase-change temperature zone by changing the temperature rise rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is an electron microscope image of phase change microcapsules.

[0022] Figure 2 This is a graph showing the change in viscosity of the phase change microcapsule suspension over time.

[0023] Figure 3 This is a graph showing the relationship between the viscosity of the phase change microcapsule suspension and the temperature.

[0024] Figure 4 It is a comparison diagram of the η-T curve under single-phase state and the η-T curve under transient temperature change.

[0025] Figure 5 is the average viscosity of the phase change microcapsule suspension and heating rate relationship curve diagram. DETAILED DESCRIPTION

[0026] The present invention is further described below with reference to specific examples, but these examples should not be construed as limiting the present invention.

[0027] Example 1

[0028] Preparation of paraffin phase change microcapsules:

[0029] 20 g of emulsifier sodium dodecyl sulfate (SDS) was dissolved in 390 ml of deionized water, and NaOH was added dropwise to adjust the pH of the solution to 7. The solution was then mechanically stirred at 300 rpm and 80° C. for 1.5 h to obtain a completely dissolved emulsifier solution. 200 g of octadecane and the obtained emulsifier solution were poured into a reactor, and sheared and stirred at 150 rpm, gear C, and 90° C. for 1 h, during which the shearing machine was stopped for 2 minutes every 20 minutes to form an oil-in-water emulsion. After the shearing was completed, Add formaldehyde resin solution and shear again for 15 minutes, then add 1.5g of melamine powder at 90°C and 300rpm, and add 3g of melamine powder for the second time after reacting for 30 minutes. Open the reactor after reacting for 1 hour, turn off the heating after 1 hour, lower the speed to 150rpm, and end the reaction to obtain a microcapsule emulsion of phase change material wrapped in a polymer shell; finally, freeze-dry the microcapsule solution under vacuum conditions on a freeze dryer for 24 hours and then grind it to prepare dry powdered paraffin phase change microcapsules.

[0030] Preparation of paraffin phase change microcapsule suspension:

[0031] Use an electronic balance to weigh 5g of paraffin phase change microcapsules and 5g of surfactant sodium dodecyl sulfate (SDS), slowly add the two to 40ml of deionized water, stir for 10 minutes, place on a magnetic stirrer, and continue stirring for 30 minutes at 30°C and 1000rpm. Then, ultrasonically disperse in an ultrasonic cleaner for 1 hour to obtain a stably dispersed phase change microcapsule suspension with a mass concentration of 10%.

[0032] The electron microscope image of the paraffin phase change microcapsules prepared above is as follows Figure 1 As shown, the particle size of the capsules is relatively uniform and the appearance is smooth and regular;

[0033] Suspension viscosity test:

[0034] At temperatures of 15°C, 20°C, 25°C, 30°C or 35°C, the shear rate range is 10-1500s -1 Within the range, the relationship between the viscosity of the phase change microcapsule suspension and the shear rate is tested at a fixed temperature. 15 viscosity points are taken every time the shear rate changes by one order of magnitude. The relationship between the viscosity of the phase change microcapsule suspension and the shear rate obtained by testing at different temperatures is shown in the η-γ curve. Figure 2 As shown, in the 600s -1 ≤γ≤1100s -1 In the range of , the suspension behaves as a Newtonian fluid with constant viscosity. This example limits the research scope to the scope of Newtonian fluid and sets the shear rate to 1000s -1 .

[0035] The shear rate was fixed at 1000 s -1 That is, the phase change microcapsule suspension is in the shear rate of Newtonian fluid, in the temperature range of 15-35℃, every 1℃, after keeping warm for 10 minutes, the multiple viscosity values ​​of the phase change microcapsule suspension changing with time are measured at a constant temperature, each temperature point is tested for 1 minute, and a viscosity point value is taken every 2 seconds. After removing the unstable viscosity point value tested in the first ten seconds, the remaining viscosity point values ​​are averaged to obtain the suspension viscosity of the microcapsule core material in the single-phase state at this temperature, thereby obtaining the relationship between the suspension viscosity in the single-phase state and the temperature, which is the η-T curve in the single-phase state.

[0036] The shear rate was also fixed at 1000 s -1, i.e. the phase change microcapsule suspension is under the shear rate of Newtonian fluid, the temperature of the microcapsule suspension is raised from 15℃ to 35℃ by heating the test platform with a heater, during the temperature rising process, the viscosity value at the transient temperature is collected, and finally the viscosity of the phase change microcapsule suspension at the transient temperature is obtained, i.e. the η-T curve at the transient temperature, the heating rate is changed, and the η-T curves at the heating rates of 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min and 7.5℃ / min are obtained, as shown in Figure 3 .

[0037] Calculation and analysis of average viscosity:

[0038] Figure 4 is a comparison chart of the η-T curve at the single-phase state and the η-T curve at the transient temperature, the viscosity curve of the phase change microcapsule suspension at the transient temperature starts to deviate from the viscosity curve at the single-phase state at a temperature and again tends to the viscosity curve at the single-phase state at a temperature, which are the starting point and the end point of the melting of the microcapsule core material, respectively, from which the phase change temperature section in which the viscosity of the suspension changes due to the phase change of the microcapsule core material can be determined, i.e. the temperature at which the melting of the corresponding microcapsule core material starts to the temperature at which the melting ends. At different heating rates, the average viscosity of the phase change microcapsule suspension in the phase change temperature section is calculated according to the following formula (1):

[0039]

[0040] wherein is the average viscosity of the phase change microcapsule suspension in the phase change temperature section, η is the viscosity of the phase change microcapsule suspension at different temperatures, T is the real-time temperature, T start is the temperature at which the melting of the phase change microcapsule starts, T end is the temperature at which the melting of the phase change microcapsule ends.

[0041] The melting start temperature T start and the melting end temperature T end of the phase change microcapsule suspension of the present embodiment at different heating rates, and the calculated average viscosity are shown in Table 1 as follows:

[0042] Table 1 Average viscosity of phase change microcapsule suspension at different heating rates

[0043]

[0044]

[0045] According to the average viscosity of the phase change microcapsule suspension in Table 1 and heating rate The relationship curve is plotted as shown in the figure Figure 5 The average viscosity of the phase change microcapsule suspension can be seen from the heating curve decreases with the increase of the heating rate , and the average viscosity of the phase change microcapsule suspension in the phase change temperature section is greater than the viscosity value of the phase change microcapsule suspension at constant temperature, thus achieving the regulation of the average viscosity of the paraffin phase change microcapsule suspension in the phase change temperature section by changing the heating rate: by changing the heating rate, the average viscosity of the phase change microcapsule suspension in the phase change temperature section can be regulated while other parameters of the phase change microcapsule suspension are controlled to be the same (the same particle size and concentration). Figure 5 The contant curve in the figure is a reference line representing the average viscosity of the microcapsule core material as a single phase, and the reference line can show that the average viscosity of the microcapsule core material as a single phase is basically unchanged.

[0046] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above embodiments, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and are all included in the protection scope of the present application.

Claims

1. A method for regulating the viscosity of an alkane phase change microcapsule suspension by using the temperature change rate, characterized in that The following steps are included: S1: Paraffin phase change microcapsules with smooth appearance and uniform particle size were prepared by in-situ polymerization, and then a stably dispersed phase change microcapsule suspension was prepared by a two-step method; S2: Within the temperature range of 15-35°C, the relationship between the viscosity of the phase change microcapsule suspension and the shear rate is obtained by testing at a fixed temperature, and the shear rate A when the phase change microcapsule suspension is in a Newtonian fluid with constant viscosity is determined; within the temperature range of 15-35°C and the shear rate A condition, multiple viscosity values ​​of the phase change microcapsule suspension that change with time are measured after being kept warm at intervals of 0.5-1°C for 5-30 minutes, and the average value of the obtained multiple viscosity values ​​is taken as the viscosity of the suspension in a single-phase state, thereby obtaining the relationship between the viscosity of the suspension in a single-phase state and the temperature, that is, the η-T curve in the single-phase state; within the temperature range of 15-35°C, the shear rate A is used and the temperature rise rate is used to test the relationship between the viscosity of the phase change microcapsule suspension and the temperature, that is, the η-T curve under transient temperature change; S3: According to the η-T curve in the single-phase state and the η-T curve under transient temperature change obtained in step S2, the phase change temperature section in which the viscosity of the suspension changes due to the phase change of the microcapsule core material is analyzed and determined, that is, the temperature from the beginning of melting of the corresponding microcapsule core material to the temperature at the end of melting; the average viscosity of the phase change microcapsule suspension in the phase change temperature section at different heating rates is calculated, and the relationship between the heating rate and the average viscosity of the phase change microcapsule suspension in the phase change temperature section is obtained, and the two show a linear relationship; the other parameters of the phase change microcapsule suspension are controlled to be the same, and the average viscosity of the phase change microcapsule suspension in the phase change temperature section is controlled by changing the heating rate.

2. The method of controlling the viscosity of an alkane phase change microcapsule suspension by utilizing the temperature change rate according to claim 1, characterized in that: The in-situ polymerization method described in step S1 specifically follows the following steps: first, add the emulsifier to deionized water, add alkaline solution dropwise to adjust the pH value to 7-10, and then stir at 200-500 rpm at 40-100°C to obtain a completely dissolved emulsifier solution; then, pour the phase change material and the emulsifier solution into the reactor, shear and stir at 50-90°C and 100-300 rpm to form an oil-in-water emulsion, then add the polymer prepolymer, react at 50-120°C to form a microcapsule emulsion with a polymer shell wrapping the phase change material; finally, the microcapsule emulsion is freeze-dried in a freeze dryer, and then ground to obtain powdered paraffin phase change microcapsules.

3. The method of controlling the viscosity of an alkane phase change microcapsule suspension by utilizing the temperature change rate according to claim 1, wherein: The two-step method described in step S1 specifically follows the following steps: weigh paraffin phase change microcapsules and anionic surfactant in a mass ratio of 1:3-0.5:1, add the two together into deionized water, stir for 5min-15min, place on a magnetic stirrer, stir for 20-40min at a speed of 100-2000rpm at a temperature of 20-35°C, and finally ultrasonicate for 0.5-3h to obtain a phase change microcapsule suspension with a mass concentration of 5%-10%.

4. The method of controlling the viscosity of an alkane phase change microcapsule suspension by utilizing the temperature change rate according to claim 2, wherein: The phase change material is at least one of a linear alkane compound and a linear alkane halide, and the high molecular prepolymer is one of a melamine resin, a formaldehyde resin or polymethyl methacrylate.

5. The method of controlling the viscosity of an alkane phase change microcapsule suspension by utilizing the temperature change rate according to claim 1, wherein: The measurement of the multiple viscosity values ​​of the phase-change microcapsule suspension over time in step S2 is performed after the suspension is kept at 0.5° C. for 10 minutes.

6. The method of controlling the viscosity of an alkane phase change microcapsule suspension by utilizing the temperature change rate according to claim 1, wherein: The particle size of the microcapsules in step S1 is 0.5 μm-30 μm, the viscosity test temperature range in step S2 is 10-35 ° C, and the shear rate is 100-5000 s -1 , the temperature change rate is 0.1-15℃ / min.

7. The method of controlling the viscosity of an alkane phase change microcapsule suspension by utilizing the temperature change rate according to claim 1, wherein: The calculation formula for the average viscosity of the phase change microcapsule suspension in the phase change temperature range is: in is the average viscosity of the phase change microcapsule suspension within the phase change temperature range, η is the viscosity of the phase change microcapsule suspension at different temperatures, T is the real-time temperature, and T start is the temperature at which the phase change microcapsules begin to melt, T end It is the temperature at which the phase change microcapsules end melting.

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